An error is raised if a CREATE TABLE statement with the WITHOUT ROWID clause lacks a PRIMARY KEY. One can write "WITHOUT rowid" or "without rowid" or "WiThOuT rOwId" and it will mean the same thing.Įvery WITHOUT ROWID table must have a PRIMARY KEY. For example: CREATE TABLE IF NOT EXISTS wordcount(Īs with all SQL syntax, the case of the keywords does not matter. To create a WITHOUT ROWID table, simply add the keywords "WITHOUT ROWID" to the end of the CREATE TABLE statement. There are sometimes space and performance advantages to omitting the rowid. However if the phrase "WITHOUT ROWID" is added to the end of a CREATE TABLE statement, then the special "rowid" column is omitted. The WITHOUT ROWID Optimization 1.0 Introductionīy default, every row in SQLite has a special column, usually called the " rowid", that uniquely identifies that row within the table. The C language interface to SQLite Version 2 Upgrading SQLite, Backwards Compatibility Locking And Concurrency In SQLite Version 3 NULL Handling in SQLite Versus Other Database Engines If it is really necessary, this problem can be solved by building a computer column and an index on it, but this is out of the scope of this article.An Introduction To The SQLite C/C++ InterfaceĬ-language Interface Specification for SQLite The reason is that, if there is an index on the summary column, it cannot be used because the query optimizer cannot make assumptions on the results of the expressions. Nothing prevents us to use those expressions in a WHERE clause or in an ORDER BY clause, but this may heavily affect performance. In the examples above, the expressions should be relatively fast (though, of course, it can be a problem when applied to a huge number of rows). It’s not used with LEN() because the case obviously doesn’t affect a string length. In both cases, LOWER() is applied before REPLACE(), to make it work when. (LEN(summary) - LEN(REPLACE(LOWER(summary), LOWER('France'(,''))) / LEN('France') LEN(summary) - LEN(REPLACE(LOWER(summary), LOWER('x'), ''))Īny number of characters, case insensitive: SELECT Single character, case insensitive: SELECT We can make them case-insensitive by using the LOWER() function. The above expressions are case-sensitive. If there are zero occurrences the expression will still work, because zero divided by any number returns zero. So, for example, if the length difference is 6 there is one occurrence, and if the length difference is 12 there are two occurrences. Returns the length difference divided by the length of ‘France’.Deletes the occurrences of ‘France’ from the superstring and counts the characters again.(LEN(summary) - LEN(REPLACE( summary, 'France',''))) / LEN('France') If we don’t know the length of the substring, the expression to use is a bit more complex: SELECT Returns the difference or, in other words, the number of x’s.Ĭounting the occurrences of a substring of any length.
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